* feat(cli): report each construct's source file on deploy

`checkly deploy` now sends an optional `sourceFile` on every resource
envelope: the path of the file that declares the construct, relative to
the git repository root with posix separators. Checkly persists it so it
can open pull requests against the right file without scanning the repo.

- Constructs declared in `checkly.config.ts` report the config file's path.
- Outside a git repository, or for files outside it, the field is omitted.
- The repo root is resolved via a new `getGitRepoRoot()` and deliberately
  kept out of `GitInformation`, which is sent to the API verbatim.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WwZUrSrvYbmAseT1wCvk8e

* fix(cli): resolve the repo root from the worktree and harden sourceFile

- getGitRepoRoot walks up to the nearest .git entry instead of using
  git-repo-info's root, which reports the main checkout inside a linked
  worktree and would attribute files to the wrong tree.
- resolveSourceFile only rejects a real `..` segment and honours the
  injected platform separator end to end.
- loadChecklyConfig restores the previously active check file rather
  than clearing it; a test pins that config-declared constructs record
  the config file and resolve relative paths against it.
- sourceFile moves to DeployResourceSync so the shared ResourceSync used
  by the import plan response does not advertise it.
- util.spec asserts the exact key set of repoInfo.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 5 <noreply@anthropic.com>